Coil winding machine



Ap 5, 1949,. G. w. GILMAN ETAL con, WINDING IACHINE 5 Sheets-Sheet 1 Filed NOV. 15, 1944 a um p bo .om

INVENTORS. Gfoeef M GILMAN GbeDo/v LA/Nq foms Glass MM, HTTO/VY April 5, 1949. G. w. GILMAN ET'AL COIL WINDING MACHINE 5 She ets-Sheet' 5 Filed Nov. 15, 1944.

THOMAS 3 67556 ATTOP/VEY Patented Apr. 5, 1949 COIL WINDING MACHINE George W. Gilman, Janesville, and Gordon F.

Laing and Thomas B. Gibbs, Delavan, Wis., assignors to The George W. Borg Corporation, Chicago, Ill., a Acorporation of Delaware `Application November 15, 1944, Serial No. 563,522

39 Claims.

The present invention relates in general to coil winding machines and more in particular to winding machines which are adapted to wind single layer coils of resistance wire on strips of insulating material for the manufacture oi rheostats and potentiometers. The object of the invention is to produce a new and improved coil winding machine of this character.

A standard strip for use in vpotentiometers may be made of Micarta or other suitable insulating material and may be, for example, 5% inches long, 116 of an inch in width, and al; of an inch in thickness. The resistance wire may be Nichrome or any other suitable resistance wire and is usually of v'ery small diameter. Bare Wire is used and accordingly the turns of the coil or winding must be spaced apart along the strip. The strip is wound straight and after the terminals are attached it is bent to a circular formation, the strip being flexible, and is suitably mounted in the casing or frame of the potentiometer. A rotatable slider is also mounted on the frame and is adapted to engage the turns of the winding successively as the slider is rotated. Y

A strip Wound with resistance wire as mentioned in the foregoing constitutes a resistance element and the complete assembly including the resistance element and slider constitutes a variable resistor or potentiometer. These devices have a very Wide application in electrical circuits. The characteristics of the resistance element vary with the application and accordingly dilerent lengths and sizes of wire are used. The number of turns of course varies with the length of the wire, assuming a standard strip is used, and the spacing of the turns will generally vary with the size of the wire. In a given resistance element the spacing of the turns may be uniform, meaning a constant number of turns per unit length of the resistance element, or the spacing may vary over the whole or part of the length of the resistance element. There may be, for example, a progressively decreasing spacing from one end to the other, producing a resistance element which will cause the potentiometer in which it is used to have a non-linear resistance characteristic. Non-linear rheostats and potentiometers are also made by employing resistance elements having tapered resistance wires and in such resistance elements the spacing of the turns may be uniform or non-uniform. In case a uniform spacing is used the non-linear resistance characteristic will be contributed solely by the 5 tapered wire, while if a non-uniform spacing is used the non-linear characteristic will be due in part to the spacing and in part to the tapered wire and results may be secured which would be diicult if not impossible with either one of these 10 i actors alone.

The various problems arising out of the foregoing are solved by the present invention. The coil winding machine disclosed herein is adapted to wind a large variety of coils, or resistance elements, With straight or tapered wire of any size which is suitable for the purpose, and with any desired number of turns within theflimits imposed by the size of the wi-re and the length of the strip. The turns in the coil ofi any resistance element, moreover, may have either a uniform or a non-uniform spacing and if the spacing is nonuniform it may Vary in any desired manner as predetermined in accordance with the desired resistance characteristic of the potentiometer in which the resistance element is to be used.

Another problem arises out of the fact that the resistance wire in general use for resistance elements is hard and must be Wound under considerable tension in order to make the shape of the coils conform to the cross-section of the strip.

The amount of tension required for this purpose depends on the size of the wire. The maximum amount of tension whichcan be used also depends on the size of the wire and for any given wire is greater than the tension required to form the coil, as will be obvious. However, in the case of these relatively ne resistance wires the diierence between the amount of tension that can be used, as limited by the breaking strength of the wire, and the amount of tension which must be used in order to produce a tight coil is not so great as might be expected, and it follows that the tension which is suitable for one wire is sufficient to break a somewhat smaller one and is entirely unsuitable The invention takes care of the tensioning problem by a new and improved arrangement whereby the tension may be regulated or adjusted to the proper value for winding resistance wire of any size that is practicable to use. In

winding a coil with resistance wire of uniform cross-section the same tension as determined by the initial adjustment is maintained throughout the winding operation, but in winding a resistance element with tapered wire the tension is automatically changed as the winding operation proceeds and at any instant it has a value which is correct for the section of the wire which is then under tension. The new tensioning arrangement also includes means for smoothing out the Variations in tension which would otherwise result from the fact that the wire is wound on a flat strip.

The foregoing and other features of the invention will be described fully hereinafter, reference being had to the accompanying drawings, in which- Fig. 1 is a plan view of embodying the invention;

Fig. 2 is a front elevation of the same;

Fig. 3 is a section on the line 3 3, Fig. 1, showing the tension adjusting mechanism;

Fig. 4 is a section through one of the collets for holding a strip during winding thereof;

Figs. 5 and 6 show a cam and supporting means thereof which is part of the tension regulating mechanism.

Fig. '7 shows a friction device for the wire spool sha/ft;

Fig. 8 shows the stop and catch for the guide wheel supporting arm;

Fig. 9 shows a resistance element comprising a coil winding machine 4a strip of insulating material with a winding of resistance wire;

Fig. 10 shows details guide Wheel;

Fig. 11 shows the changeable gears for driving the strip advancing cam;

Fig. 12 is a section on the line I2-I2, Fig. ll;

Fig. 13 is a section on the line |3-I3, Fig. 11; and

Fig. 14 is a diagrammatic circuit drawing showing the electrical connections for the motors and switches.

Referring to the drawings, the various parts of the coil winding machine are supported on a base I0, which may be the top of a table or bench. The bed I I is preferably a steel casting and is provided with legs at the ends by means of which it is supported on the base I0. The shape of bed II can be seen from Figs. 1, 2 and 3.

The headstock I1 and the tailstock I8, so-called because of their resemblance to the headstock and tallstock of a lathe, are slidably mounted on the bed I I in the usual manner and are connected together by means of the rod I9, Fig. 2, so that they always move together. This rod is threaded to enable the distance between headstock and tailstock to be adjusted. Locknuts are provided as shown.

The tailstock is provided with two integrally formed upright bearing members and 2|, which rotatably support the spindle 22. At its right hand end the spindle has the collet 23 for holding one end of a strip of insulating material while the same is being wound. The construction of the spindle and collet may be explained in connection with Figs. 1, 2 and'4.

The spindle 22 is tubular and is -bored out at the end to a larger internal diameter to receive the collet 23. The latter is a slotted cylindrical member having an axial bore of the proper size to receive the rod 25, said bore being enlarged and provided with internal threads for a part of its length to receive the threaded sleeve 24. This of the strip support and sleeve is made of tubular stock and has a few threads at the left hand end by means of which the nut 26 is attached. The nut 26 affords means whereby the sleeve may be rotated to engage its right hand threaded end with the internal threads of the collet 23 in order to secure the latter in position at the end of the spindle.

The rod 25 is the operating member for the pivoted latch 21 and has a sloping cam surface at the end for engaging the V shaped projection on the lower side of the latch. The latch 21 is located in a slot in the collet 23. This slot is intersected by a threaded hole having a diameter greater than the width of the slot and in which there is a spring 29 for exerting e, pressure on the latch to hold it in normal position. The spring is compressed between the latch and the screw The end of collet 23 is slotted as indicated at 3| and there is an insert 32 which has a. corresponding slot the width of which is the same as the width of the strips to be wound. The rod 25 is normally maintained in the position in which it is shown in Fig. 4 by a spring 34, Figs. 1 and 2, which surrounds the rod between the nut 26 and the knob 33 which is attached to the end of the rod. In order to operate the latch 21 the knob 33v is pressed to the right, causing the end of the rod to engage and lift the latch, and thereby raise the pin 28 far enough so that the end thereof clears the slot 3 I.

The spindle 22 is driven by the gear is secured to the spindle and is in mesh with the wide faced pinion 39. The spindle is not only rotatable but is longitudinally movable also, and to effect the latter type of movement a forked lever 38 is provided, pivotally mounted on the post 40 which extends vertically upward from the tailstock. The bifurcated end of lever 38 carries two pins disposed on opposite sides of the spindle and projecting into an annular groove in the sleeve 31, which is xed to the spindle. A spring 36 is compress'ed between the hub of gear 35 and the bearing member 2I and normally, that is, when no strip is in the machine, maintains the spindle in its extreme left hand position, with the shou1der 4I engaging the bearing member 2I, as shown in Fig. 4. The spindle is moved to the right against the force of spring 36 by means of 1ever 38, as will be readily understood.

The headstock I1 is provided with the two integrally formed ybearing members 42 and 43, which rotatably support the spindle 44 having the collet 45 at the left hand end thereof. The construction of spindle 44 and collet 45 is similar to the construction of spindle 22 and collet 23 just described, except that spindie 44 has no longitudinal movement in its bearings. The means for effecting such movement is omitted therefore and spindle 44 is somewhat shorter than spindle 22. For driving spindle 44 the gear 46 is provided. This gear is fixed to the spindle at a. point between the bearing members 42 and 43 and is in mesh with the wide faced pinion 39. The knob 41 is for operating the latch in the collet 45 and corresponds to knob 33.

The spindles 22 and 44 and their associated collets alford means for holding a strip at its opposite ends and for rotating the strip to wind a wire thereon, as will presently be explained in detail. The wire is delivered to the strip at a fixed point past which the strip is moved lengthwise by a sliding movement of the headstock and tailstock on the bed II. At the point where the wire is delivered additional supporting means for the strip is provided and will now be described.

35 which 46 which spans the bed Referring to Figs. 1, 2 and 10, there is a bracket I I and'has the integrally formed bearing 49 and the two feet 50 and 5I which rest on ledges projecting from the sides of the bed. The bracket is secured to the bed by screws which pass through holes in the feet and are threaded into tapped holes in these ledges. The gear 52, which meshes with the wide faced pinion 39, is supported on the hub 53 which is rotatable in the bearing 49. Opposite the gear 52 the hub 53 supports the circular plate 54, which is held in position by machine screws passing through the gear and hub as shown. The plate 54 is the additional support for the strip and has a centrally located slot 55 in which the strip has an easy sliding t. i l

The reference character 56 indicates a motor which is mounted on the base I0. The motor 56 drives the shaft 60 by means of pulleys and a belt 51, there being a plurality of pulleys of different sizes at each end of the drive to provide for rotating shaft 60 at different speeds. The shaft 60 has bearings in the two lbrackets 59 and 6I which are secured to the rear side of the bed II and extend upward for a short distance above it as can be'seen in Fig. 2. The bracket 6I has a for. ward extension 65 at the top which provides a bearing for one end of shaft 62. This shaft has another bearing in-the bracket 66 which is secured to the rear side of the bed I I near the other end thereof. Shaft 62 is driven from shaft 60 by means of gears 63 and 64 and carries the wide faced pinion 39, hereinbefore referred to, which is adapted to rotate spindles 22 and 44 and the supporting plate 54 by means of gears 35, 46 and 52 respectively. It will be noted that the gears are all of the same size so that the spindles and supporting plate are driven in synchronism, and it will be observed further thant the arrangement described provides a drive for the spindles in all positions of the headstock and tailstock.

In Figs. l and 2 the headstock and tailstock are shown in an intermediate position. They are movable in either direction by means of compressed air under control of the valve 61. The arrangement includes an air cylinder having a piston slidable in the cylinder and a piston rod 1I which is suitably coupled to the headstock I1 as indicated. An air pipe 69 supplies compressed air to the valve 61, which has a v a left hand operated position in which compressed air is supplied to the right hand end of cylinder 10 and`a right hand operated position in which compressed air is supplied to the left hand end of cylinder 10. Movement of the valve handle to the left accordingly moves the headstock and tailstock to the left and vice versa. The limit4 of movement to the right is established by the engagement of the piston with the right hand end of the air cylinder. Movement to the left is limited by the cam 11, as will be explained presently. The valve 61 is so constructed that when air is admitted to either end of the air cylinder the other end of the cylinder is vented to the atmosphere by way of the eX- haust valve 68. This valve is kept partly closed so as to compel a gradual exhaust of air from the cylinder and thus provide a cushioning effecteto preventthe jar that would otherwise occur when the parts reach the limit of their movement in either direction.

At the left hand end of the bed II there is a heavy casting which is supported partly on the base I6 and partly on the bed, being secured to the latter by bolts as shown in Figspl and 2.

neutral position, l

This casting comprises the end plates I2 and I3, bottom plate I4 and the two webs I5 and I6. The shaft 62 extends to the left beyond its bearing in bracket 66 and passes through the end plate I3 `of the casting, where it.has another bearing. By means of a plurality of gears which will be described more in detail presently, shaft 62 drives the shaft 12, which has a bearing at the end plate I3 and another bearing 16 which is suitably supported on the bottom plate I4 as indicated in Fig. 2. Shaft 12 drives the shaft 13, which has bearings in the webs I5 and I6, by means of a worm 14 and worm gear 15. Shaft 13 supports the cam 11. The shaft is of larger diameter where it passes through the bearing in the web I6, whereby shoulders are formed against which the worm gear 15 and cam 11 are clamped by means of nuts 18 and 19, the enlarged portion of the shaft being slightly longer than the bearing to provide enough clearance so that the shaft can turn freely.

The cam 11 controls the. advance of the tailstock and headstock during winding operations and to this end is provided with a follower having a roller 6I engaging the periphery of the cam. The follower 80 is connected to the tailst'ock I8 by a rod 83 .and is slidably supported on the member 82 which in turn is supported on the web I6 as shown. The follower 86 has a dovetail connection with the member 82, similar to the connection between the tailstock, for example, and the bed I I.

The gearing for connecting shaft 12 with shaft 62 may now be briefly, described with reference to Figs. ll, 12 and 13.-

As previously mentioned, the shaft 62 has a bearing at the end plate I3. This bearing is indicated at 89 in Fig. l2 and has a lining 90. The bearing is secured to the end plate by machine screws as shown. The gear 86 is keyed on shaft 62 beyond the bearing and is held in position by a washer and the nut 9I-.

The bearing 89 not only supports the shaft 62 but also forms a pivot for the sector85, which is angularly adjustable on the bearing and is retained in any adjusted position by the stud or bolt 92 which passes through a slot in the sector and is threaded into a boss on the end plate I3.` The sector 85 carries two sets of gears which are supported on two adjustable studs 93 and 94. The details ofthe mounting of one of these sets of gears comprising gears 81 and 88 may be explained in connection with Fig. 13.

The stud 9 3 has a flange 99 which bears against the sector 85. Beyond this ange the stud is threaded and carries the nut 91 which is located in the slot 98. This slot is stepped and the nut comprises a shank portion which fits the narrow part of the slot and a head which fits the wide part. The nut is square so it cannot turn in the slot but it is movable along the slot to adjust the position of the stud 93. After the stud has been properly located the nut is tightcned up by applying a wrench to the squared end |69 of the stud. This clamps the sector 85 between the head of the nut 91 and the flange 99 on the stud and fixes the stud rigidly on the sector.

The sleeve 95 is rotatable on the stud 93 and has a slot extending lengthwise thereof in which there is fixed a key 96. AThe gears 81 and 88 are carried on the sleeve 95 and have keyways for the key 96. The key and sleeve therefore effectively couple the gears together so that they rotate as a unit. A suitable washer and a nut slipping on' the stud.

The arrangement including stud 94 for mount- J ing'the other set of gears on sector 85 is the same .f

as described. It will shown are readily changeable or smaller diameter and that in any case proper meshing of the gears can be effected by adjustment of the sector 85 on its pivot and adjustment of the studs in their slots.

The shaft 12 carries the gear |02 and has a bearing supported on the end plate 3 which is similar to the bearing for shaft 62. The bearing for shaft 12 also supports the sector |03 which is similar to sector 85 and carries two sets of gears mounted on the adjustable studs |04 and |05. The arrangement will be clear from the explanation alreadyvgiven.

The two gear sets mounted on sector |03 are not always used. If not required to produce the necessary gear ratio between shafts 62 and 12, these gears are omitted and the inner gear stud 94 is meshed directl with the gear such as |02 on shaft 12.

The reference character indicates an aux-l iliary base resting on the base I0 and supporting the motor The auxiliary base ||0 also supports a pedestal ||2 which is provided near the top with suitable bearings for the shaft |3. This shaft-is driven by the motor through the medium of a worm on the motor shaft and a worm gear ||6 on shaft ||3. The drive is irreversible. At the end opposite the worm gear ||6 the shaft ||3 is arranged to carry a wire for gears of larger spool such as which can be clamped against a shoulder on the shaft by a knurled nut 4.

The wire spool end of shaft I3 is shown in Fig. 7. About half way between the shoulder and the point where the threads start a transverse hole is drilled in the shaft. The drilling operation is stopped as the point of the drill breaks through, leaving an annularvlip which retains the ball ||1. A spring ||8 is compressed between the ball and the screw ||9 and tends to maintain the ball in the position in which it appears in Fig. 7. When 'a wire spool is placed on the shaft the ball is forced into the shaft and presses against the wall of the hole in the spool, forming a friction device which prevents the spool from spinning freely ,on the shaft before the nut is tightened up. The reason for the provision of this friction device will be explained presently.

The reference character indicates an upright post or standard which is suitably xed to the base I0. At the top the post |20 carries the member |2|` on which the arm |22 is pivotally supported. This arm is preferably made of light wood so as to keep its weight as low as possible. The clevis |33 and the pulley |34, supported on the end of arm |22, are preferably made of aluminum for the same reason. The arm |22 is slotted at its pivoted end to provide for attachment of the metallic extension |23. The spring |24 is tensioned between the end of the extension |23 and the member |25 on post |20 and tends to rotate the arm |22 on its pivot far enough to bring the upper end of the spring into alignment with the pivot and the lower end of the spring.

-The rod is slidably supported by the member |25 xed to post |20, that is, the rod has a bearing in this member in which it is longitudinally movable. At its upper end the rod |'30 carries a block |29 of insulating material on which the contact springs |21 and |28 are be noted that the gears mounted, is supported on mounted. The spring |28 is adapted for actuation to engage the other spring by a cam member |26 which is fixed to the side of arm |22.

'I'he lower end of rod |30 extends downward through an opening in the base I0 and is pivotally connected to one end of the lever |35. This lever is supported on the bracket |36 and has its other end pivotally connected to the rod |31, which extends upward through an opening inthe The rod |31 is slidably supported by the bracket |38 which is mounted on the front side of the bed The bracket |38 also supports a. fixed post |39 which extends upward parallel to rod |31. The member |40 is slidable on post |39 and has an extension in front provided with an opening for the rod |31, the end of which is threaded for the nut |43.

The position of the member |40 slotted holder |46 by set screws, and the holder.

-This force is communicated to rod |31 by the lever |35 and tends to move the rod |31 and the slidablemember |40 downward, thereby holding the roller 4| in engagement with the cam |42. Thus the cam is able to control the position of the switch |`21-|28 relative to the switch actuating cam |26 on arm |22. 'I'he position of the switch determines the tension in the wire when it is wound on the strip, as willbe made clear in the explanation of the operation of the machine.

The reference character |50 indicates a guide wheel for delivering the wire to the strip on which it is being wound. As shown in Fig. 3, also in Fig. l0, the guide wheel |50 is mounted on a pivoted arm |5|, which in turn is supported on the bracket 48. The details of this construction are shown in Fig. 10, from which it will be seen that the shaft |53, on which the guide wheel |50 is the arm |5| by means of ball bearings. These bearings should be carefully adjusted for free rotation of wheel |50 but without play in the bearings. The arm |5I' is supported by ball bearings on the flanged stud |54 which passes through the bracket 48 and is held in place by a nut. The stud is squared at the end so that it can be held by a wrench while the nut is being tightened up. A helical spring |55 has one end secured to the arm |5| and the other end secured to the stud |54 and is tensioned to rotate the arm in a counter-clockwise the movement of the arm |5| is arrested by a stop |56 formed on the block |51 located between arm |5| and bracket 48 and secured to the latter by a machine screw. The tension in spring 55 is adjusted by loosening the nut on the stud |54 direction or the other until the spring has the proper tension. The nut is then tightened up to hold the stud in adjusted position.

The block |51 has a hole drilled therein to receive the latch |58 and has a slot for the operating pin |60 which is secured to the latch. The spring |59 is compressed between the pin |60 and the bracket 48 and forces the latch to the left,

9 Figs. 8 and 10, as far as such movement is permitted by pin |60. The latch is provided to hold the guide wheel |50 out of the way while a strip is being inserted in the machine. When the arm is pulled forward it becomes engaged by the latch in an obvious manner and later on is released by moving the operating pin to the right.

As shown in Fig. 3, the arm |5| has a forward extension |52 which carries the pulley |6|'.

The guide wheel |50, arm I5| and extension |52 are made as light as possible consistent with the necessary strength, to enable the guide wheel to maintain contact with the strip during the winding operation. The rotation of the strip causes the arm |5| to oscillate on its bearing and by keeping the inertia of the arm and associated parts low the requisite movement is made possi- 'ble with only a moderate tension in spring |55.

At the rear of the bed two brackets |65 and |66 are attached and project horizontally to the rear. The rod |61 is slidably supported in these brackets and carries the two adjustable collars |68 and |69. A switch comprising the contact springs |1| and |12, Fig. 14, and enclosed in the housing |13, is secured to the end of the bed and is adapted to be operated by the rod |61. The rod is moved to the right and left by means of a member secured to the tailstock |8 and having a depending projection |10 which is adapted to engage the collars |68 and |69 on rod |61. Near the end of the movement of the tailstock to the left the projection |10 engages the collar |`68 and moves the rod |61 to the left to open the switch. To avoid any danger of damaging theswitch the rod |61 has a spring biased retractable pin |14 at the end for engaging the switch actuating member. The switch is self-closing and in order to prevent it from closing at once when the tailstock starts to move to the right a friction device in the form of a spring |15 bearing on rod |61 is provided. When the tailstock reaches nearly the limit of its movement tothe right the projection |10 engages the collar |69, which moves the rod |61 to the right and permits the switch to close.

The wiring of the machine is shown in Fig. 14. The motors 56 and may be alternating current motors of known type. The circuit of motor 56 includes the hand operated switch |8| and the switch |1|-|12, these switches being in series. The circuit of motor is similar and includes the hand operated switch |80 and the switch |21|28. The hand operated switches are mounted at a convenient point on the base I0, as shown in Fig. l.

A seat is provided for the operator and is preferably located in front of the machine as it appears in Fig. 1 and about in line with the motor The parts of the machine which have to be attended to are thus directly in front of the operator and the valve 61 vand switches |80 and |8| can easily be reached with her right hand.

The operation of the machine will now be described. For this purpose it will be assumed that the machine is set up for winding standard strips with tapered resistance wires. The resistance wires are supplied on spools such as ||5. Each spool contains one tapered resistance wire wound on the spool in a single layer.

In Figs. 1 and 2\ the machine has been shown with the headstock and talstock at approximatelv the center of their travel on the bed, but this has been done to avoid obscuring the collet 45 on spindle 44, which in the normal position of the machine is inside the hub 53 on which the 10 gear 52 is supported. From this it will be understood that the machine normally stops with the headstock and tailstock assembly in its extreme left hand position. The machine has also been shown with a strip held in the collets, although the insertion of the strip has not been explained. The strips are changed in the normal positiOn of the machine.

In order to advance the machine to normal position the operator may move the handle of valve 61 to the left and close the switch |81. The operation of the Valve admits compressed air to the right hand end of air cylinder 10, thereby applying a force to the headstock and tailstock assembly which tends to move it to the left. Such movement is prevented by cam 11, but the air pressure holds the roller 8| of follower 80 against the cam. The closure of switch |8| starts the motor 56 which drives the shaft 60 by means of belt 51. Shaft 60 drives the shaft 62 through the medium of gears 63 and 64 and shaft 62 drives the cam shaft 13 by means of gears 86, etc., shaft 12, worm 14 and worm gear 15. Shaft 62 also drives the spindles-22 and 44 -by means of the wide faced pinion 33, also the support 54, but the operation of these parts may be neglected for the moment as the operator is merely engaged in advancing the machine to normal position.

The cam shaft 13 is rotated in-a clockwise direction as seen in Fig. 2, and the cam 11 accordingly permits the headstock and tailstock assembly to move gradually to the left, under the air pressure in cylinder 10. This movement continues until the 'projection |10 on the tailstock |8 engages the collar |68 on rod |61 and moves the rod to the left to open the switch |1||12 and stop the motor 56. When the machine stops the cam 11 will have rotated about 180 degrees from the position in which it is shown in Fig. 2. The strip is inserted from the left as seen in Figs. 1 and 2. One end of the strip is passed through the slot 55 in the intermediate supporting plate 54 and into the slot at the end of collet 45 on spindle 44. These slots are in angular alignment. As the strip enters the collet the end of the strip engages the sloping end of the pin at the end of the latch (see Fig. 4 for the corresponding parts of collet 23) and raises the pin and latch by a Icam action. rl`he strip thus passes beneath the pin, 'which drops into the holein the strip as soon as the hole comes into alignment with it, thereby locking the strip against withdrawal from the collet. The other end of the strip is now just outside collet 23. To cause the strip to enter the collet 23 the operator grasps the lever 38 and moves it to the left, thereby moving the spindle 22 and collet 23 t0 the right. At the same time the end of the strip is guided into the slot at the end of the collet. As the collet `m0ves to the right the pin 28 slides up on the strip and then drops into the hole in the strip. The operator now releases the lever 38, whereupon the spindle is returned toward the left by spring 36 `far enough to take up the slack, if any, in the connections between the strip and the collets. The strip is now held between the two collets and is under tension produced by the force of the'compressed spring 36.

It should be stated that before starting to insert the strip as described in the foregoing the operator will pull the arm |5| forward to get the guide wheel |50 out of the way. The arm |5| is locked in its forward position by the latch |58.

The operator may now swing the handle of the valve 61 to the right, which admits compressed 11 air to the left hand end of cylinder and connects the right hand end of the cylinder with the exhaust valve 68. As the result the headstock and tailstock assembly is moved quickly to the right as far as it can go, or until the piston engages the end of the cylinder. The gradual exhaust of air from the right hand end of the cylinder maintains sufficient back pressure to prevent excessive shock when the movement is arrested. As the headstock and tailstock assembly approaches .the end of its movement to th eright,

the projection |10 on the tailstock engages the collar |68 on rod |61 and moves the rod to the right, thereby releasing the switch |1||12 and permitting it to restore to its normal closed position.

The closing of switch |1||12 restarts the motor 56 and the machine starts to run again as previously described. 'In the movement of the headstock and tailstock assembly to the right the follower 80 moves to the right also, of course, the follower being attached to the tailstock. The distance through which the parts move to the right is slightly greater than the rise on the cam 11, and it will be understood therefore that in the right hand position now occupied by the follower 80 the roller 8| is out of the way of the high end of the cam. In this connection it should be V'pointed out that the collar |69 should be so adjusted that the motor circuit is not closed until the necessary clearance has been effected.

The starting position is indicated by an arrow on the cam. 'I'he operator watches the cam as it rotates and as soon as the arrow reaches a position in alignment with the center of the roller 8| she stops the machine by opening the switch |8|. In case of overrun, or error in operating the switch, the cam can be brought to the correct position by means of the hand wheel 58, but a practiced operator has no difficulty in stopping the machine properly so that no adjustment is necessary. The angular distance between normal position and starting position depends on how much of the cam is used. Assuming that 340 degrees of the cam are used, then the distance is degrees.

The operator may now swing the handle of the valve 61 to the left, admitting compressed air to the right hand end of the cylinder 10 and moving the headstock and tailstock assembly to the left. The movement is short and is stopped by the roller 8| engaging the cam 11.

If not already done the operator now takes a spool 5 containing a tapered resistance wire and places the spool on the shaft ||3. The nut ||4 is put on also but is not tightened up, leaving the spool free to rotate on the shaft except for the friction device described in connection with Fig. 7.

The resistance wire usually includes an end section several feet long which is of uniform diameter, then a tapered section in which the cross-section of the wire progressively decreases according to some predetermined formula or equation, and finally another end section of uniform diameter. In winding the wire on a strip the winding is started with the large end of the wire. During the manufacture of the wire the large end section is marked with paint or in any suitable manner to advise the operator of the winding machine where to start to wind. This mark is placed at the proper distance from the beginning of the tapered section to insure that the tapered section will be properly located on the strip when the winding is completed.

f wheel 58, rotating the .I strip |85 over the |5| on which the The ends of the resistance wire may be secured in notches in the flanges or heads of the spool. After detaching the large end of the wire, the operator pulls the wire off the spool until she finds the mark and then cuts the wire off at this point. The part cut off is discarded. The wire is then passed over the pulley |34 and the end is secured to the collet 23 by means of a small spring clip |86, shown in Fig. 4. During this operation the necessary amount of wire is drawn off the spool but only as much as required is unwound, due to the friction device which prevents free rotation of the spool. The operator now operates the machine by means of the hand strip |85 to wind on a few rather widely spaced turns. The hand wheel is rotated with one hand and with the other hand the operator guides the wire onto the strip. Three or four turns will be suilcient to bring the wire to a point on the strip which is opposite the guide wheel |50. The operator now places the wire on the guide wheel |50 and pulley |6| and turns the spool l5 back enough to take up the slack. The wire, indicated at |81 in Fig. 3, passes from the guide wheel |50 and under the pulley |6|. The guide Wheel and pulley are grooved. After the operator has seen to it that the wire is properly located in the grooves and has taken up any slack that may be present so that the wire cannot become dislodged she can tighten up the nut ||4 to secure the spool H6 to the shaft I3 on which it is supported.

'I'he operator may now move the latch |68 to the right by means of pin |60 to release the arm guide wheel |50 is mounted. Arm 5| accordingly is rotated on the stud |64 by spring |55 to bring the guide wheel against the strip. The machine is now ready to start winding the wire on the strip but before proceeding with the explanation it will be advisable to direct attention to the condition of the wire tensioning means.

Since the machine is in starting position the headstock and tailstock assembly is displaced to the right from the position in which it is shown in Fig. 2 and the cam |42 likewise, with the result that the roller |4| is now resting on the high horizontal part of the cam rather than on the sloping portion thereof. The rod |31 is therefore raised and the rod |30 is correspondingly lowered from the position in which these parts appear in Fig. 3. In view of the position of rod |38, the block |29 and the switch |21-I28 which are supported on the rod are also in a lower position. The exact position of these parts at this time depends on the adjustment, which is effected by means of nut |43 on rod |31, as will be explained presently. It will be suflicient for present purposes to state that at the start' the switch I 21|28 is low enough so that the arm |22 has to rotate on its pivot a substantial amount from the horizontal, say 15 or 20 degrees, in order to close the switch. As regards the present position of this arm, if the operator has merely taken up the slack in the wire, the end of the arm will be elevated due to the tension in spring |24 and the lever extension |23 will be substantially parallel with the post |20. The operator may be instructed, however, to tighten up the wire enough so as to bring the arm |22 substantially to a horizontal position. The spring |24 will therefore supply a certain amount of initial tension to the wire.

In further explanation of the cam |42 4it will be understood that the sloping section of the cam corresponds to the tapered section of the resistance wire. The base of this sloping section of the cam is equal or substantially equal in length to the section of the strip |85 on which the tapered section of the wire is to be wound, and the cam is so adjusted lengthwise relative to its support that when the machine is winding the tapered section of the wire on the strip the roller I4I will bear on the sloping section of the cam.

Proceeding with the explanation of the winding operation, the operator should close the switch |80 in the circuit of motor III, if this switch is not already closed. The motor does not start, however, since the switch I21-I28 is open. The operator may now close the switch I8 I which starts the motor 56, switch I1|-|12 now being closed. The machine now starts to run. The

two spindles 22 and 44 and the supporting plate 54 are rotated simultaneously and positively rotate the strip |85 to Wind the wire |81 thereon in successive turns, while at the same time the cam 11 rotates slowly to controll the advance of v the headstock and tailstock assembly to the left and thus space the turns apart on the strip. The Winding speed may be about 350 turns per minute.

When the winding starts, the wire for the rst couple of turns or so is necessarily taken from the loop which extends upward to pulley I34 at the end of arm |22,` since the spool |I5 cannot rotate the motor III, and the shortening of this loop draws :the pulley I34downward, thereby rotatingarm |22 on its pivot. The rotation of the arm results in further tensioning of the spring |24, and since the force required to produce the rotation is applied through the wire, it is placed under an increasing tension as the rotation of the arm takes place. The rotation of the arm continues for a few degrees, as explained hereinbefore, until the cam |26 engagesthe spring |28 and forces it into contact ywith spring |21.v This operation closes the circuit of `motor II'I which begins to run and rotate the spool II5, thereby feeding the wire off the spool and relieving the tension in the wire suficiently to prevent further rotation of the arm |22.

The demand for wire varies periodically at the winding frequency, due tothe fact that the wire is being wound on a flat strip. The periodic variation in the demand for wire causes the arm |22 to vibrate during the winding operation and the cam |26 alternately closes and opens the switch I21-|28, which automatically regulates the spoed of motor III to maintain the proper tension in the Wire. I-f at a certain instant the motor runs a little too slow, for example, producing too much tension in the Wire, the average position of arm |22 is lowered slightly, thereby increasing the ratio of the time during which the switch is closed to the time during which it is open and increasing the amount of power delivered to the motor. The motor therefore increases its speed, feeds out the wire faster, and the tension is decreased. If this action proceeds too far, it is corrected by the resulting change in the average position of arm |22, whichcauses the power supplied to the motor to be cut down, as will be readily understood.

, at pulley |34.

The wire is delivered to the strip by the guide wheel |50, which maintains contact with the strip during the winding operation. It will be understood, therefore, that the guide wheel has an oscillatory motion. i The guide wheel is pressed against the strip by the spring |55, aided by the tension in the wire. As regards the eifectof the wire tension it will be seen from Fig. 3 that the pulley IIiI is located somewhat'to the right of an imaginary line drawn between the pivot of arm |5I and the point where the wire leaves the pulley The strip is supported close adjacent the guide`v wheel by the plate 54. The plate is driven in synchronism with the spindles and thus helps to rotate the strip, but the spindles alone bring about the longitudinal movement of the strip, which slides in the slot in the plate as the winding proceeds. The firm support which the rotatlng plate 54 aords to the strip at the point where the wire is delivered is a large factor in the successful operation of the machine.

As explained before, the winding is started at a certain predetermined point on the large end section of the wire, the unused portion of which is cut off. The remainder of this end section, which may be a foot or more in length, is wound on the strip first, followed by the tapered section, which may be fty feet or more in length. During the time that the end section of the wire is being wound on the strip the roller` I4I rides on the high horizontal part of the cam |42 and a uniform strong tension is maintained on the wire. As the winding proceeds the cam moves to the left` under the roller and as the winding of the tapered section of the wire begins the sloping pontion of the cam reaches the roller. From now on and until the winding of the tapered section is completed the roller rides on the sloping portion of the cam, with the result that the tension on the wire is gradually decreased.

The decrease in the tension is caused by the raising of the switch I21-I28, through the medium of its connection with roller I4I, and the resulting counter-clockwise rotation of the arm |22, which decreases the tension in spring |24. The tension on the wire is always equal to one half the force exerted by the spring, as measured The decrease in the wire tension is approximately proportionate to the decrease in the cross-section of the tapered Wire and to its breaking strength.

When the winding of the tapered section of the .Wire has been completed the machine starts to wind the small end section and at this time the roller I4| begins to ride on the low horizontal part of cam |42. From this point on therefore the tension on the wire does not change.

When the required number of turns of the small end section have been wound on the strip the machine is stopped by the opening of switch I1I-I12 aspreviously described, which opens the circuit of motor 56. The motor I I stops an instant later, or as soon as enough Wire has been fed off the spool to relieve the tension sufliciently so that the switch I21-I28 remains open.

The "operator may now cut off the wire a few inches from the strip and detach the starting end from the clip |86 on the collet 23. In order to release the strip from the collet the operator moves the spindle 22 slightly to the right by means of the lever 38 and then presses the knob 33 to the right to raise the latch in the collet. While the knob 33 is held in operated position the lever is released, whereupon the spindle is moved to the left by spring 3B until the shoulder 4| engages the side of bearing 2|. The left hand end of the strip is now outside the collet. The operator now momentarily presses the knob 41 to the left-to raise the latch in collet 45 and removes the wound strip from the machine. The ends of the winding are suitably secured, as by looping them through the holes at the ends of the strip or by the application of a spot of adhesive. This finishes the strip insofar as the winding thereof is concerned. The operator may now insert another strip in the manner explained and shift the handle of the air valve 61 to the right. The headstock and tailstock assembly accordingly moves to its right hand position and closes the switch |1l-l12, which starts the motor 56 to advance the machine to starting position.

While waiting for the machine to reach its starting position the operator may remove the spool H5 from which the Wire just wound has been taken and replaced it with another spool containing another resistance wire,

When the Imachine reaches its starting position, as indicated by the mark on the cam 11, the operator stops the machine as before by opening the switch 8|. The air valve handle is now moved to the left to bring the roller 8| of follower 8U against the cam. The operator now passes the end of the new resistance wire over pulley |34 and attaches it to the collet 23 by means of clip |86, then loops the wire over the guide wheel |50 and under the pulley |6l, takes up the slack in the wire and secures the spool by means of nut H4, all as previously explained. During these operations the switch |80 may remain closed, since the circuit of motor is open at switch |21-|28. The winding of the second strip is now ready to proceed and is started by closing the switch |8|. The operation from now on is a repetition of the operation performed in winding the rst strip and will require no further explanation.

The general appearance of the wound strips is shown in Fig, 9, where |85 indicates a strip of insulating material and |81 indicates a resistance wire wound thereon. The drawing is not intended to show the size of the wire nor the actual number of turns or spacing thereof. It does, however, indicate a progressively decreasing spacing of the turns. The wire may be tapered or of uniform diameter throughout its length, although in the present case a tapered wire has been assumed. The machine is adapted to wind very fine Wire, and coils have been successfully wound using untapered wire as small as .9 mils in diameter. This is about the smallest size wire that it is practicable to make. Tapered wires may be 6 or 8 mils or larger at the large end and may be as small as .9 mils at the small end, with any form of taper. The number of turns which can be wound on a given strip depends on the spacing of the turns, and on the size of the wire. A strip wound with wire .9 mils in diameter may have 500 or more turns per inch.

Some further explanation regarding the setting up and adjustment of the machine may now be given. The most complicated case to -be considered involves the Winding of a resistance element for a non-linear potentiometer having a resistance curve which requires the use of a tapered resistance wire and a. non-uniform turn spacing which supplements or modifies the effect of the taper.

In order to wind a resistance element such as described above the cam 11 must be of special design, adapted to produce the required spacing. A suitable procedure for making the cam will therefore be explained briefly.

In a typical case which will be assumed by way of example, the specification covering the potentiometer gives the length of the resistance element, that is, the length of the winding, the total resistance 0f the resistance wire, and the resistance of each of 20 imaginary sections of equal length into which the winding is divided for the purpose of dening its resistance characteristic.

The first step is to obtain the data on the resistance wire which is to be used. The resistance of this wire must be, of course, equal to the specied resistance. The data required includes information as to the length of the wire and a resistance curve or the equivalent which shows the exact form of the taper.

From the resistance curve of the wire to be used and the specied resistances of the winding sections the length of wire in each section is calculated. The length of a turn is known from the size of the strip, which enables the number of turns in each section to be calculated from the length of wire in such section. The total number of turns in the winding is also calculated from the length of the wire and the known length of a. single turn.

The next step is to divide the working portion of the cam into 20 imaginary sections corresponding to the winding sections and calculate the number of degrees in each cam section from the number of turns in the corresponding winding section. In this connection it will be evident that since the cam is geared to the spindles which rotate the strip the number of degrees in any cam section will be proportionate to the number of turns in the corresponding winding section. Any desired part of the cam can be used, up to about 350 degrees, but 340 degrees is the amount generally used. Dividing the total number of turns by 340 gives the number of turns per degree, and dividing the number of turns in any winding section by the turns per degree will give the degrees in the corresponding cam section.

Now the total rise on the cam over the working portion thereof, 340 degrees, is equal to the length of the winding, which is known. Dividing the total rise by 20 the rise per section is obtained.

The information now at hand as to the length in degrees of each of the 20 sections which make up the 340 degree working portion of the cam and the further information as to the rise per section enables the designer to fix 20 points on the cam, in addition to the starting point, and this will usually be sufficient to enable him to lay out the entire contour of the cam.

For winding coils having uniformly spaced turns a straight line cam is used, ,the design of which presents no difliculty. In a straight line cam there is a uniform rise per degree over the whole Working portion of the cam.

The gear ratio is obtained by dividing the total number of turns in the winding by the number of rotations of the cam. The cam always makes less than one complete rotation, and in the assumed case rotates 340 degrees. So the number of turns is divided by the fraction 340 over 360 to obtain the total speed reduction required. Shaft 62 rotates at the same speed as the spindles, but there is a to 1 reduction between shaft 12 and shaft 13. The total speed reduction is therefore divided by 100, and the result gives the speed reduction which must be obtained between shafts 62 and 'l2 by means of the gears 86, 81, etc. The machine is supplied with sufficient gears of various sizes so that by interchanging gears the desired reduction can be obtained.

The starting point for the machine is marked on cam 11, as previously mentioned. The mavtached to the machine. proper amount of tension for wires of diiferent chine is set to stop at the right point by running it from the starting point and counting the number of rotations of shaft l2 with a rotation counter. "Prior to this operation the collar I on rod itl is loosened up so that the rod cannot be operated to stop the machine. When the counter indicates a number of rotations which is equal to the number of turns in the winding the machine is stopped manually by opening the switch lll and the collar III is adjusted and locked on rod |61 in the correct position so as to just barely open switch Ill-|12.

v'll'iie rise on the cam |42 depends on various factors involvedfin the design of the wire tensioning mechanism, such as the lever ratio in the linkage, the length of arm |22, etc., and is preferably determined by experiment. It will be understood, however, that the rise will be at least roughly proportionate to the taper on the wire, that is to the difference between the large and small diameters of the wire. For example, a greater rise will be required for a wire which tapers from 8 mils toA .9 mils than for one which tapers from mils to .9 mils.

The contour of the cam should conform generally to the contour of the taper. If the taper is conical or not too far from conical the contour of the cam may be a straight line. The square ratio between the diameter of the wire and its cross section or breaking strength is taken care of by the design of the lever`arrangement for operating the switch |2l|2l, including the spring |24. This part of the apparatus is so designed that within the operating range of arm |22 (about 45 degrees) the force required to rotate the arm from its uppermost or zero position to any new position is approximately proportionate to the square of the. distance from the zero position to the new position.

, The wire tension is preferably adjusted before winding starts and before the rst wire is at- For this purpose the sizes is determined experimentally or by calculation, and weights of corresponding value are provided. In the case of a tapered wire the wire tension employed most .nearly approaches the breaking strength of the wire at the small end,- there being a considerably greater factor of safety at the large end, and the tension adjustment is accordingly made in accordance with the small diameter of the wire. In order to make the adjustment the headstock tailstock assembly is shifted to its left hand position, if not already there, to cause the roller |4| to ride on the low horizontal part of cam |42. The appropriate weight is then hung on the end of arm |22 and 2. In a coil winding machine, means for holding and rotating a flexible strip of material, a rotatable support for said strip ilxed against movement lengthwise o! the strip, means for delivering wire to said strip at a point adjacent to said support to form a coil on the strip responsive to its rotation, and means for moving said holding means to thereby advance said strip longitudinally relative to` said support to space the turns of the coil.

i 3. In a coil winding machine, two devices for holding a ilexible strip of material at its opposite ends, respectively, a supporting device for said 'fstrip located at a point intermediate of said the nut |43 on rod |31 is adjusted up or down until the cam |25 just barely closes the switch l2l-l2l. When the adjustment is finished the weight is removed. f

The invention having been described that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appended claims.

We claim:

1. In a coil winding machine. means for holding and rotating a strip adapted to form a support for a coil, means for delivering wire to said strip at a fixed point to form a coil on the strip responsive to its rotation, and means for progressively advancing said holding and rotating means to move said strip past said fixed point in timed relation to the rotation ofthe 'strip in order to l space the turns of the coil.

holding devices, and means for positively driving all said devices at the same speed. v

4. In a coil winding machine, two shafts in axial alignment, means at the adjacent ends of said shafts for holding a flexible strip of material at the opposite ends thereof, a rotatable device for supporting said strip at a variable point intermediate of the ends thereof, means for positively driving said shafts and said device at the same speed, and means for axially moving said shafts independent of said device to change the point at which the strip is supported by the device.

5. In a coil winding machine, means for holding and rotating a strip of material adapted to form a support for a coil, means including a guide wheel for delivering wire to said strip to -wind a coil thereon responsive to rotation of the strip, means for pressing said wheel against said strip during the winding of said coil, and means for moving said strip past said wheel to space the turns of said coil.

6. In a coll winding machine means including two spindles in axial alignment for holding and rotating a strip of material to wind a coil thereon, supporting means for said spindles, said supporting means being movable to produce axial movement of said spindles, a uid operated actuator for said supporting means, and means including a cam rotating in timed relation to the rotation of said spindles for controlling the speed with which said supporting means moves under the power supplied by said actuator.

7. In a coil winding machine, a device for `holding and rotating a strip of material to wind `the rotation of said device.

8. In a coil Winding machine, a device for holding a strip ofmaterial adapted to form a support for a coil, a motor for rotating said strip to wind said coil thereon, a movable support for said device, means driven by said motor for controlling the movement of said supportl to space the turns of said coil, and a switch actuated by movement of said support to control the circuit of said motor.

9. In a coil winding machine, means for holding and rotating a strip adapted to form a support for a coil, means for delivering a wire to said strip to form a coil on the strip responsive to rotation thereof, means for longitudinally moving the strip relative to the point at which the wire is delivered to space the turns of the coil, and means for automatically changing the speed at which the strip is moved to vary the spacing.

10. In a coil winding machine, means for holding and rotating a stripradapted to form a support for. a coil, means for delivering a wire to said strip to form a coil on the strip responsivev strip to form a coil on the strip responsive to rotation thereof, means for axially moving said strip relative to the point of delivery to space the turns of the coil, and means for progressively slowing down the rate of axial motion of the strip while maintaining the rotationalspeed constant, thereby progressively increasing the number of turns per unit length along the coil.

l2. In a coil winding machine, means for winding a tapered wire on a strip to form' a coil having a plurality of spaced turns, means for placing said wire under tension at the start of the winding operation, and means for automatically varying the tension in accordance with the change in the size of the wire as the winding proceeds.

13. In a coil winding machine, means for holding and rotating a strip of material, means for delivering a tapered wire from a spool to said strip to form a coil on the strip responsive to rotation thereof, and means for maintaining a varying tension in that section of the wire which extends between the spool and the strip which at any instant is proportionate to the size of the wire in said section.

14. In a coil winding machine, means for winding a tapered wire on a strip to form a coil having a plurality of spaced turns, said coil being started with the larger of the two ends of the wire, means for placing the wire under an initial tension which is appropriate for the larger end of the wire but excessive for the smaller end, and means for automatically decreasing the tension as the winding proceeds.

15.v In a coil winding machine, a device for holding and rotating a strip of material adapted to form a support for a coil, means for delivering a tapered wire to said strip to wind a. coil thereon responsive to rotation of the strip, a support for said device, means for moving said support in timed relation to the rotation of the strip to space the turns of the coil, means responsive to rotation of the strip for placing the wire adjacent thereto under tension, and means including a cam moving with said support for varying the tension.

16. In a coil winding machine, means for holding and rotating a strip to form a coil thereon from a wire contained on la spool, means for preventing said rst means from rotating said spool by pulling on said wire, means for rotating said spool to permit said wire to be unwound from the spool as it is wound on the strip, and means responsive to tension in said wire for controlling said rotating means.

17. In a coil winding machine, means for holding and rotating a strip to form a coil thereon from a wire contained on a spool, means for preventing said rst means from rotating said spool by pulling on said wire, means including a motor for rotating said spool to permit said wire to be unwound from the spool as it is wound on the strip, means for placing the wire between the spool and strip under a varying tension which increases responsive to rotation of the strip and 20 decreases responsive to rotation of the spool, and means responsive to a predetermined tension for closing the circuit of said motor.

18. In a coil winding machine, means for holding and rotating a strip to form a coil thereon from a wire contained on a spool, means including a motor for rotating said spool, an actuator subject to vibration responsive to the varying pull on the wire produced by rotation of the strip, and a switch intermittently closed and opened by said actuator at its vibration frequency to supply power to said motor.

19. In a coil winding machine, means for holding and rotating a strip to form a coil of wire thereon, means including a motor for feeding the wire to said strip, a pivoted arm arranged to be rotated by the pull on the wire as it is wound on said strip, a spring opposing rotation of said arm to tension said wire, a switch operated responsive to rotation of said arm to start said motor, and means for changing the relation between said switch and said arm to regulate the tension produced in said wire by said spring.

20. A non-linear resistance element comprising a strip of insulating material having a winding of tapered wire, said wire being under tension, and the degree of tension at different points along said element being proportionate to the size of the wire at such points.

2l. The method of winding a tapered resistance wire on a strip to form a resistance element, which consists in rotating the strip to wind the wire thereon, feeding the wire to the strip at a limited rate, applying a force to the section of wire between the strip and feeding means to place such section under tension, and adjusting the force to change the tension in accordince with the change in the size of the wire in such section as the winding operation proceeds.

22. The method of winding a tapered resistlance wire on a strip to form a resistance element, which consists in rotating the strip to wind thev wire thereon, feeding the wire to the strip at a fixed point, moving the strip longitudinally with reference to said point to space the turns of the winding, and changing the rate of said longitudinal movement with respect to its rotational speed to produce a varying spacing which bears a predetermined relation to the slope of the taper on the wire.

23. 'I'he method of winding a resistance wire on a strip to form a resistance element, which consists in rotating the strip to wind the wire thereon, feeding the wire to the strip at a limited rate, maintaining a loop in the wire between the strip and feeding means, opposing an increasing force to the shortening of the loop which results in case the demand for wire by the rotating strip exceeds the rate of feed, thereby maintaining the wire in the loop under a tension which is proportionate to the length of the loop, and increasing the feed if the tension becomes greater than a predetermined value.

24. In a coil winding machine, means for holding and rotating a supporting element for a coil, means for delivering wire to said element to form a coll thereon responsive to rotation thereof, spacing means including a cam and follower for controlling movement of said holding and rotating means to advance said element past the point where the wire is delivered thereto, and means for driving said cam at a speed which bears a predetermined relation to the rotational speed of said element. l

amasar 25. In la coil winding machine, a base, a device slidably mounted on said base, means in saiddevice for holding and rotating -a supporting element to wind a coil thereon, means including' a cam for controlling the sliding movement of said device, means for rotating said cam in timed relation to the rotation of said element, and means responsive to the arrival of-sald device in a predetermined position for stopping the rotation of said element.

26. In a coil winding machine, a device for holding a supporting element f or a coil, means including a cam for controlling movement of said device to cause a longitudinal movement of said element, means for rotating said cam, means in said device including a spindle 'geared to said cam for rotating said element to wind a coil thereon in spaced turns, means for stopping the rotation of said spindle responsive to a predetermined extent of movement of said device, and means for readily changing the gear ratio between said cam and spindle to enable the machine to wind coils which diier as to the number of turns contained therein.

27. In a coil winding machine, means for winding a wire on to a supporting element to form a coil thereon having a plurality of spaced turns, and means operated in timed relation to the progress of a winding operation for controlling the spacing of said turns to produce a varying spacing which is independent of the wire size and which is greater in one section of said coil than in an adjacent section.

28. In a coil winding machine, means for winding a wire on to a supporting element to form a coil thereon, and means for spacing the turns of said coil apart as the coil is wound, said means including an element which is adapted to produce a predetermined varying spacing and which is readily interchangeable with a similar element adapted to produce a different predetermined varying spacing.

29. In a coil winding machine, means for winding a wire on to a supporting element to form a coil on the element having a plurality of turns, wire guiding means for delivering the wire to said element, means for producing a relative movement between said element and guiding means to space said turns, and means including a cam for controlling said movement, said cam having an operative contour which is effective to produce a spacing which varies from turn to turn according to a predetermined law.

30. In a coil winding machine, means for winding a length of tapered wire on a support to form a coil having a plurality of turns, means for placing a section of said wire adjacent said support under tension during the winding operation, and means including a cam having a rise corresponding to the slope on said wire for automatically regulating the tension in accordance with the size of the wire in said section.

3l. In a coil winding machine, means for winding a tapered wire on a support to form a coil having a plurality of turns, means for placing a section of said wire adjacent said support under tension during the winding operation, and means operated in timed relation to the progress of the winding operation for regulating the tension in said section in accordance with the size of the wire therein.

32. In a coil winding machine in which coils are wound from wire contained on a spool, a motor, an irreversible driving connection between 22 said motorl and said spool,l whereby said motor' can drive said spool but said spool cannot' drive said motor, a circuit for said motor, and means responsive to a predetermined pull on the wire by operation of said' machine for closing said circuit.

33. In a coil winding machine, means for holding and rotating a supporting element to wind a coil thereon from wire contained on a spool, means for forming a loop in the wire between said element and spool, said means including a lever having one arm to which a force is applied by the wire in said loop, a spring adapted to apply an opposing force to another arm of said lever, said lever and spring being so arranged that the ratio of the spring arm to the loop arm of the lever increases responsive to rotation of the lever on its fulcrum, and means actuated by rotation of said lever for controlling the rotation of said spool to feed the wire.l

34. In a coil winding machine, means for winding a wire on to a support from a supply spool to form a coil on the support, a motor for rotating said spool to feed the wire oi the spool, means including a switch for supplying power to said motor, a switch actuator movable toward said switch by tension in said wire between said support and spool, a spring opposing such movement, and means for adjusting the position of said switch relative to said actuator to enable the switch to be closed responsive to a selected wire tension.

35. A coil winding machine as claimed in claim 34, wherein means is provided for automatically changing the position of said switch to vary the wire tension during a winding operation.

36. The method of winding a resistance wire on a core or support to form a resistance element, which consists in rotating said support to wind the wire thereon, feeding the wire to the support at a fixed point, moving the support longitudinally with reference to said point to space the turns of the winding, and changing the rate of the longitudinal movement of said support with respect to its rotational speed to produce a varying spacing which gives said resistance element a non-linear resistance characteristic.

37. In a coil winding machine in which coils are wound from wire contained on a spool, a motor, an irreversible driving connection between said motor and spool, whereby said motor can drive said spool but said spool cannot drive said motor, and means for regulating the speed of said motor in response to changes in the pull on said wire caused by operation of said machine.

38. In a coil winding machine in which coils are wound from wire contained on a spool, means for positively driving said spool to feed wire to said machine, including means for preventing rotation of the spool independent of the power supplied by said driving means, and means responsive to the pull on said wire by operation of said machine for regulating the speed of said driving means.

39. The method of winding a resistance wire on a core or support to form a resistance element, which consists in rotating the support to wind the wire thereon, positively feeding the wire to the support independent of the pull on the wire caused by the winding operation, maintaining a section of the wire between the support and feeding means under a varying tension which increases or decreases depending on whether the winding speed or the rate of feed is the higher,

, 23 and regulating the rate of teed responsive to Number changes in the tension in said section. 1,773,709 GEORGE W. GILMAN. 1,857,817 GORDON F. LAING. 1,887,808 THOMAS B. GIBBS. 5 1,939,902 2,023,603 REFERENCES CITED 2,058,525 The following references are of record in the 2'314'070 nie of this patent: 2'315'904 10 2,331,662 UNITED STATES PATENTS 2,353,639

Number Name Date 1,314,909 Sleeper Sept. 2, 1919 1,357,773 Greenewalt Nov. 2, 1920 Number 1,675,650 Grout July 3, 1928 163,072 1,755,314 Caxter Apr. 22, 1930 24 Name Date Daniels Aug. 19, 1930 McCann May 10, 1932 Havlish Nov. 15, 1932 Kaul Dec. 19, 1933 Lodge Dec. 10, 1935 Takanashi Oct. 27, 1936 Bogoslowsky Mar. 16, 1943 Pizzi et al Apr. 6, 1943 Delano Oct. 12, 1943 Berthold July 18, 1944 FOREIGN PATENTS Country Date Great Britain May 2, 1921 

